Within the context of test and measurement instruments such as digital storage oscilloscopes (DSOs) and the like, signals under test (SUT) are digitized using an analog to digital (A/D) converter to provide sample data suitable for further processing, such as waveform generation. Several types of A/D converter configurations are in wide use, such as, successive approximation, fast-in slow-out (FISO) and flash (A/D) converters. The typical flash converter consists of a set of comparators that produce a “thermometer code” output. This is then converted with several levels of combinational logic directly into a binary number value that represents one sample. FISO A/D converters store samples in a bank of capacitors. One acquisition is obtained at a high sample rate, then the charges are multiplexed out at a slower rate to a conventional A/D converter.
In typical oscilloscope architectures, speed of conversion is sacrificed in order to reduce power requirements. Pipelining techniques are sometimes used to regain some of the lost speed. In order to obtain very high sample rates, multiple A/D converters may be interleaved. The FISO approach requires the use of a complex timing and correction algorithm that is applied to the data after it is digitized.
Current oscilloscope digitizers have equivalent time and interleave modes of operation. Binary samples from digitized SUTs are stored in large circular waveform memories. Acquiring a waveform requires interaction from a system processor that manages the resetting of hardware registers as well as the computing of trigger positions and the unloading of wrapped waveforms in the circular memory. As a result, the dead time between trigger events can be very large.